1. Field of the Invention
The invention relates to a device and method for handling workpieces, in particular vehicle chassis.
Such a system comprises a handling line having a plurality of successive handling regions in which the workpieces are introduced for surface treatment.
A handling region may, for example, be an immersion tank containing a treatment fluid, but the term handling region may be defined as any kind of booth or tank whenever a workpiece undergoes treatment therein. Such treatment may include, for example, a washing operation. Other examples include immersion phosphating, pre-treatment for immersion coating, powder coating, wet-paint coating and the like.
2. Prior Art
Previously known devices for the surface treatment of workpieces such as vehicle chassis in immersion baths or treatment booths are divided into continuously conveying devices and discontinuously conveying devices.
In the case of continuously conveying systems, the chassis are fastened inside suspension gear and a chain drive is used to convey them along the handling line, lower them into the immersion baths, convey them through the immersion baths and lift them out of the immersion baths again. A continuously conveying system for the surface treatment of vehicle chassis is described in DE 196 41 048 A1. In this device, the vehicle chassis are each held by rotary frames that are moved a fixed distance apart from one another at a uniform speed with the aid of a common conveying means above a plurality of treatment tanks. The vehicle chassis are introduced into and removed from the immersion baths by means of a selective rotational movement that can be coupled rigidly, via guide rails, to the translatory movement of the rotary frames. The rotary frames are guided by a revolving chain system and are therefore guided rigidly in relation to one another and at a continuous speed, both in the region of the handling line above the immersion baths and during return travel.
Discontinuously conveying systems are known in the prior art, too and are referred to as cyclical systems. In the case of cyclical systems, the vehicle chassis are moved on article mounts over the immersion baths, stopped there and dipped into the treatment bath with the aid of lifting means, such as hoists or swivel gear, and, after the process time has elapsed, the chassis are lifted or swivelled out of the bath again.
An example of such a system is described in DE 43 04 145 C1 or DE-U-200 22 634.7.
Choosing between a continuously conveying device and a discontinuously conveying device must take account of the specific pros and cons of both basic ideas. For instance, the continuously conveying devices are more reliable because their operation requires fewer drive motors, whereas the individually timed article mounts of cyclical systems are more likely to malfunction as a result of the plurality of individually controlled motors. The maximum throughput of workpieces per time unit in the case of continuous devices is, furthermore, higher than that of cyclical systems. The advantage of cyclical systems, on the other hand, is the high degree of flexibility regarding workpiece handling as a result of the ability to individually drive the individual article mounts.
In the automotive sector, efforts are being made to operate the systems with high throughputs. At the same time, however, a high degree of process flexibility is desired as well, because once a system has been set up in an automotive plant, it may be intended to perform different workpiece-handling operations in the future.